Presently known arithmetic calculators are generally unique input devices which are either keyboard operated, that is, by depression of keyboards keys, or do not involve a keyboard and are operated responsively to electrical data signals. The former variety are of desk-top type or hand held with a keyboard inclusive of numeric keys and so-called function keys, for example, decimal point (.) key, add (+) key, subtract (-) key, multiply (.times.) key and equals (=) key, or like end of computation key. Numeric information is first entered by depression of the numeric keys successively in decreasing order (hundreds, tens, units). The decimal point function key is next operated and thereafter the numeric decimal information is entered by depression of the numeric keys successively in decreasing order (tenths, hundredths, thousandths). The numeric information thus keyed into the calculator is transferred into the calculator arithmetic processor part by depression of one of the remaining function keys as the occasion demands. Thus, for entries preceding the final entry in a summation, the add function key is operated after the data is set up. For the final entry, it is customary to depress the equals function key to complete the summation and display the result thereof while clearing the processor part for further use.
Data entry discipline for the keyboard calculator is thus completely accomplished by the operator. Misoperation, such as key rollover, i.e., operation of keys to enter succeeding data during entry of current data, is simply observed on occurrence and corrected by the operator.
In the non-keyboard type of calculator, data entry discipline is controlled by various complex arrangements of circuitry and software adapted to sequentially shift data to arithmetic processing circuitry without intervention of the operator.
Applications arise at times for which the above-discussed unique input calculators are unsuited. For instance, where the numeric information is largely operator enterable with but an occasional resort to numeric information available only in electrical data signals, the desk-top or hand held calculator and the non-keyboard calculator are each independently insufficient and cost considerations may preclude the presence of both devices.